Production of metal hydrides



March 27, 1945. p, P ALEXANDER 2,372,168

PRODUCTION oF METAL HYDRIDES Filed March 5, 1943 f BY Patented Mar. 27, 1945 1.. t ,L fagzgsg 1, A

j PRODUCTION'QF METAL Hypnimss 1 ileter Alexander, rlllarblehread, Mass.,l asslgnor ,i v. V

to Metal Hydrides Incorporated, Beverly, Mass, t,

acorporatlon of Massachusetts geclaimd This inventiony relatesv to the production of sub-" stantiallypure metal hydrides andhas for its ob` ject more-particularly theproduction of substantially pure metal hydrides from hydride-forming metalsof comparatively low boiling point which are contaminated with metal'impurities of lower boiling point. 1 t y n y y It is known thata numb'erof vmetals,react directly with hydrogen at :a sufficiently high `tem-v perature tov -rform corresponding metal hydrides.

The purity of themetal"hydride 'conforms to' that of the krnetalrused `to make the""`hydride. rInf a standard gradeof electrolytic calcium, for ex,-L ample, which' has anaverage [Purity of "about 90%, is used, the resulting'- calcium hydride jwill 'also have apurity ofabout 90% :I berjzaatusedurlngfthe` ciuxn,'strontium"an`d barium',` are usually madek by subjectingtheirnfused chlorides to electrolysis. Since the ysaltsio'f the'r alkali metals, `sodium and potassium, arel usually present in these chlorides, the resulting alkaline earth metal is usually contaminated with a small amount of alkalilmetal, as well as oflthe chlorideoi the alkaline `earth metalitself.v uTo purify the alkaline earthmetal,` it' has been proposed to subject the metal todistillationl in a closed retort that has been` evacuated to removeobjectionable air. `The distilled metalis permitted to condense in a cooler part of the retort,usually in the form oa more or less` spongydeposit. rAfter cooling the retort,` air is admitted, the retort is opened and the condensed metal'is removed.` rIjhe vresulting product is so re active that it frequently oxidizes rapidly on the i, (Giza-+204); c n y other retort; ther retort is closed,A filled With'hy` `drogen and heated untilthe hydrogen reacts with the calcium to i form substantially pure calcium hydridelf These operationsare vdangerous and require considerable-time;

As aresult of y'my investigations, I have discov` ered that these disadvantages may be rovercome for the most part.v The alkali metals, sodium and potassium, may bedistilled and segregated from the alkaline earth metals in a `form to make them `no`ninflam`mableon' exposure tothe oxidizing influence of air-'.3 IThe'alka'tline earth metal' likewise may be distilled and separately collectdl and at? the same time be 'substantiallyfreed of its chloride. Thealkaline earth metal is preferably retained in the'retort in whichit is distilled and converted into calcium hydride insitu.

Inaccordance with the invention, a

airto atemperature at which the metal impurity is distilled. The resulting-*metal impurity vapor is selectively oxidized byfbringing it into reactive contact with; a metallic oxide located away from the main body. of the Ihydride-`forming metal. The oxidized metal impurity is collected'asa solid separatefrom the hydride-forming metal. The nydride-.forming metal is itself distilled and condensed as a solid separate from the oxidized metal impurity and hydride-forming metal residues.l The condensed lhydride-'forming metal is brought to a temperature at which it reacts with `hydrogen, after which it is brought into reactive con- .tact with hydrogen Vuntil it is converted to metal. hydride. The substantially pure metal hydride is then suitably recovered.

lThese and other features of the invention may be better understood by referring to the accompanying drawing, taken in conjunction with'the following description, in which:

Fig. 1 is a diagrammmatic representation, being l a side elevation in section, offan apparatus with surface and 'produces lheat insufficient amount' toigni'te the whole mass, with the result that fires are quite common. This objectionable lresult is all the more apt t'o occur becausehof the presence of the more highly' reactivev alkalimetals, sodium and potassium. `These alkali metals are also distilled'and condense in a cooler part` of the retort.` The small deposits of sodium `and potassium' are so'reactive that` they almost" invariablycatch yfire when'the retort is openedandthey come incorr-` tact with vthe oxygenoi air'. i If by skillful manip-` ulation thacondensed cialium` removed. suc: cess'fully from t thefre'tort,A it is then placed in t an#l furnace.` The retort preferably consists of heat which the method of the invention may be practiced; and

Fig. 2 is a horizontal section on the line 2-2 of Fig.1,'\ vThe apparatus shown comprises an outer retort lsupport'ed'within a heating'furnace H,th`e` retort being rheld in position Ibi/"means of twor or more supports"l2 resting" on top'of the heating resistantsteel: Itis tted with areniovable cover I3 having attached Atiueretoa vertical pipel4,

provided-with lateral vaived'branches is and is, mnciebl? with 'agvur iof, hydra-gen, Tend.

I hydrider` forming? metal contaminated withmetal impurity of lower boiling point is heated in the absence of i helium, respectively, and a vertical valved branch I4', connectable with a source of vacuum. A removable inner retort 20, having an open top, fits within the outer retort. A removable tray 2| rests over the open top of the retort, being supported thereon by means of three or more lugs 22 extending over the wall of the inner retort. The heating furnace ll consists essentially of a rectangular chamber 23 having a refractory bottom 24, side and end walls 25, and a top 26 having an opening of a size adapted to receive the outer retort. An expanding opening 21 is provided 'at or near a lower corner of one of the side walls of the chamber, for the introduction of heating gases into the chamber. A similar opening 28 is preferably provided at cr near an opposite corner, as a spare or auxiliary means for introducing heating, or cooling, gases into the chamber. When not in use, the opening 28 is closed. A flue opening 29 extends through the same wall as the opening 21, preferably at a higher level, so that heating gases passed into the chamber through the opening 27 tend to pass almost completely around the retort before leaving the chamber through the ue opening 29.

The apparatus may be used as follows: A charge of calcium, for example, contaminated with sodium, potassium, and calcium chloride, is placed in the bottom of the inner retort 20. The inner retort is then placed in the outer retort l0. A layer f titanium oxide 30 is placed in the tray 2l, which is in turn placed across the open top of the inner retort. The removable cover i3 is placed on the outer retort l0 and locked thereon to provide a sealed joint. The vertical branch I4' is then connected to a source of vacuum. With the valve of this vertical branch open, and the valve of the lateral branches i and I6, closed, the outer and inner retorts are placed under vacuum to remove objectionable air.

Heating gases are passed through opening2'l into the heating chamber, where they circulate almostcompletely around the retort and then pass through the ue opening 29 to the outside atmosphere. As the lower portion of the outer retort I0 is heated, the lower portion of the inner retort is also heated. As the temperature rises, a point is reached where the sodium and potassium present in the calcium are distilled. The resulting sodium and potassium vapors rise to the upper and cooler portion of the retort where they come in contact with the titanium oxide 30 in the tray 2 l Due to their great afiinity for oxygen, the sodium and potassium are promptly oxidized and the titanium dioxide is reduced to titanium and a sub-oxide of titanium according to reactions which may be indicated as follows:

As the temperature at the bottom of the inner retort continues to rise, a point is reached where the calcium is distilled and its resulting vapor tends to condense and settle out against the wall of the inner retort immediately below the tray i6. Some calcium vapor may of course rise suiilciently to come in contact with titanium dioxide in the tray and react with it in a manner similar to sodium or potassium vapor. The bulk of the distilled calcium may, however, be separately condensed and collected, as shown. A residue consisting essentially of calcium chloride, admixed perhaps with a small amount of sodium chloride 1`or potassium chloride, or both. remains as a residue in the bottom of the inner retort.

The introduction of heating gases to the heating chamber is stopped and the retort is permitted to cool. When the condensed calcium has reached .a temperature at which calcium hydride can be formed without dissociation, the vacuum is broken by opening the valve of lateral branch l5 to admit hydrogen to the interior of the retort. Suilicient hydrogen is thus introduced to permit complete conversion of the condensed calcium to calcium hydride. For this purpose, under the conditions I have operated, the retort has been allowed to cool down tc about 400 C., after which the hydrogen was admitted.

If the rf Action proceeds too rapidly, the hydrogen is advantageously diluted with an inert or neutral gas, such as helium. As dilution slows down the reaction, it may be carried on to completion under complete control. Instead of diluting the hydrogen with such a gas, the hydrogen may be admitted at a slower rate than that at which it is capable of being absorbed by the calcium. A vacuum is then automatically maintained in the retort and the speed of reaction may be slowed down as desired.

The end of the reaction is indicated when a sufficient amount of hydrogen has been absorbed by a corresponding weight of calcium. The retort is then cooled to room temperature, hydrogen is displaced by air, and the retort is opened. Since all the sodium has been absorbed by the reaction with titanium oxide and all the distilled calcium has been converted into far less reactive calcium hydride, the danger of spontaneous combustion is eliminated. The substantially pure calcium hydride is then scraped out of the retort with comparative safety.

It will be clear to those skilled in this art that the invention lends itself to numerous modifications. Strontium and barium may be similarly treated to remove sodium and potassium, and to convert these explosive alkali metals into harmless compounds. Instead of titanium oxide, other suitable refractory metallic oxides, such as zirconium oxide and chromium oxide, may be employed, either separately or admixed.

In the practice of the invention, advantage is taken of the relative boiling points of the metals. The boiling points of sodium and potassium are substantially below those of calcium, strontium and barium. The temperature of the metal to be purified is therefore gradually elevated to a point where thefmetal impurity of lower boiling point is distilled. The retort is caused to yield a graduated temperature range. 'I'his is effected by heating the bottom of the retort, and permitting the upper portion of the retort to extend above the heating chamber into the open atmosphere. Since sodium and potassium have the lower boiling points, their vapors tend selectively to rise highest in the retort. Since calcium, strontium and barium have the higher boiling points, their vapors tend not to rise as high in the retort. ".ll'hey soon meet a temperature environment conducive to condensation. In other Words, the alkaline earth metals may be made to condense in an intermediate section of the retort where the temperature is high enough to keep the alkali metals in vapor form. The alkali metal vapors, on the other hand, tend to rise to a cooler portion of the retort, where they were heretofore condensed, but where they are now converted into harmless compounds in accordance with the present invention.

'1f.gInf"-' the `method 'of `producing'siAbstantlally `pure "calcium "ih'ydridey `theLimprovement which `comprisesl heating calcium" contaminated' with e a `metal impurity of lower boiling point inthe absence of air ft'o a'-temperatfu're at which: the *metaijfimpurity' butl not thepaicium is] distiued, "selectively` oxidizingthe resulting metalimpurity vapor by bringing'itin 'reactive contactlwith a ,refractory metallic oxide removedffrom the main bodyof calcium, collecting' the oxidized-metal iln-v purity as, a solid? separate `from the calcium, distilling fthecallciuvm, condensing theresulting "calcium yvapor,asia `solid separate froml the `oxij dized metalimpurity and calcium residues; cooling the condensed `calcium* to a temperature at which it reactswith hydrogen, bringing hydrogen into reactive contact withgthe calcium until it l` is convertedto calcium hydride, and recovering the resulting substantially pure calcium hydride.

, y Method according to claim 1, in which the calcium is heated while under` Vacuum, and V,breaking the yvacuum Vafter thecalcium vapor hascondensed. i l e 3. Method according tol claim 1, in which the"r refractory metallic oxide is selected from the e group; f titanium oxide, zirconium oxide and chromium-oxide.` a 4. Method accordingzto` claim 1, in which the f metal impurity `is at least one of the group:` sol dium and potassium. u t

5. Methodaccording lto claim1,vin which the hydrogen I is diluted with an'inertgasfto slow down Vthe 'speedofreaction between the hydrogen and the condensedcalcium; i

l 6. "Method according toclaim'lyin'whichthe hydrogen yis rdiluted withhelium to slow down the speed of reactionbetween `the hydrogen and ycondensed; calcium? 'lqInthe method ofvproducing substantially *pure metal nhydride, the [improvement which comprisesfheating a jhydride-'forming metal conj taminated with 'a metaljirnpurity'offlower boiling pointin the"r absence of 'airtol a .temperature af' which. thejlmetall impurity" but 'nt the h5- ride-fgrminfmfetal is distilled, slectivelrllxi- `vdining the: 'resultingI metall impuritygvaprl c by 4bijingingit in "Jtivecontactlwith.a refractory fmetalli V"oxide moved'frfomthe [main body of y,

refractory metallic oxide is selected from the `11.` Method-y ccording Vto claim "1l-1 inl-'which the 'jhydrid'e'sformifng metal ""isheated while lunder 5 "vaciurn, and breaking the 'vacuumlafter thchy- Adrifdforming metal vaprhascondensed i `f 12";r Method according 'to' claimvv in which" the hydrogen j isf diluted with "an inertl gas to slow d rowriy the Speed 'of reaction'y between the hydro- 0 gen'andthe condensed,hydridefforming metal.V

`T13. Method according toy claim 7; inwhichthe `hydrogen' is diluted with helium tof slowdown thespeed of reaction between the hydrogen `and the condensed hydride-forming metal.

1li. Method accordingto claim-.7, in' which the jhydride-forming 'metal isvj selected from l' the group; calcium, strontium land barium; and the metal impurity is'at least 4one of thegrou'p': sodium and potassium. l5. Method accordingl to claim 7, in which the hy'dride-forming metal is` selected fromH the group; calcium, strontium and barium; `and the metal impurity is atleast one of. thegroup': vsodium and potassium; and the refractory metallic `oxide is'selected from the group: titanium oxide, zirconiumv oxide and chromium' oxide. .1 f 16. Method accordingto claim 1,*in'which the refractory `metallic oxide is selected `from the group: titanium oxide, zirconium oxide and chrokmium oxide;"and the metall impurity isiat least one of `the group: sodium andpotassium'. 3

17,- In the method of producing-substantially pure metaly hydr'ide Ifromimpure hydride-forming metal contaminated" with a metall impurity of" lower boiling point, the improvementwhich comprises placing the impure metal in a retort, evacuating the retort to remove objectionable air, heating the metal-containing" part of the retort vvabovethe melting pointv of said metal, "distilling `the metal impurity but not the metalto be purified, selectively oxidizing the resulting metalim- *purity vapor by bringing it into reactive'contact with wa re'ducible metal` oxide removed` from the '.mainbody'of,` metal to b e purified, collecting the 45 "/oxidizedmetal impurity as a solid'separat'e from "the main'bodyof metal to'be purifled; distilling landconder'ising"the "metal thus' puried in a fthef'fn'eeai "imprint ined, seletivsly corresponding metal hydride.

19. In the method of producing substantially pure metal hydride from impure hydride-forming metal contaminated with a metal impurity of lower boiling point, the improvement which comprises placing the impure metal in a retort containing in its upper part a body of reducible metal oxide, evacuating the retort to remove objectionable air, heating the metal-containing part; of the retort above the melting point of said metal, distilling the more volatile metal impurity but not the metal to be purified and absorbing the more volatile metal impurity by reaction with the metal oxide, distilling and condensing the less volatile metal thus purified in a cooler part of the retort removed from the oxidized metal impurity, admitting hydrogen gas into the retortl and continuing to supply hydrogen gas to the retort until the distilled and condensed metal is converted into the corresponding metal hydride.

20. In the method of producing substantially pure calcium hydride from impure calcium metal contaminated with a metal impurity of lower boiling point, the improvement which comprises placing the impure calcium metal in a retort, evacuating the retort to remove objectionable air, heating the calcium-containing part of Athe retort above the melting point of said calcium, distilling the metal impurity but not the calcium, selectively oxidizing the resulting metal impurity vapor by bringing it into reactive contact with a reducible metal oxide removed from the main body of calcium to be puried, collecting the oxidized metal impurity as a solid separate from the main body of calcium to be purified, distilling and condensing the calcium thus purified in a cooler part of the retort removed from the oxidized metal impurity, admitting hydrogen gas into the retort and continuing to supply hydrogen gas to the retort until the distilled and condensed calcium is converted into the corresponding calcium hydride.

21. In the method of producing substantially pure calcium hydride from impure calcium metal contaminated with a metal impurity of lower boiling point, the improvement which comprises placing the impure calcium metal in a retort, evacuating the retort to remove objectionable air, heating the calcium-containing part of the retort above the melting point of said calcium, distilling lthe metal impurity but not the calcium, selectively oxidizing the resulting metal impurity vapor by bringing it into reactive contact with a reducible metal oxide removed from the main body of calcium to be purified, collecting the oxidized metal impurity as a solid separate from the main body of calcium to be puried, distilling and condensing the calcium thus purified in a cooler part of theretort removed from the oxidized metal impurity, admitting an inert gas and hydrogen gas into the retort, and continuing to supply hydrogen gas to the retort until the distilled and condensed calcium is converted into the corresponding calcium hydride.

22. In the method of producing substantially pure calcium hydride from impure calcium metal contaminated with a metal impurity of lower boiling point, the improvement which comprises placing the impure calcium metal in a retort containing in its upper part a body of reducible metal oxide, evacuating the retort to remove objectionable air, heating the calcium-containing part of the retort above the melting point of said calcium, distilling the more volatile metal impurity but not the calcium to be purified and absorbing the more volatile metal impurity by reaction with the metal oxide, distilling and condensing the less volatile calcium thus puriiied in a cooler part of the retort removed from the oxidizedy metal impurity, admitting hydrogen gas into the retort and continuing to supply hydrogen gas to the retort until the distilled and condensed calcium is converted into the corresponding calcium hydride. 4

23. In the method of producing substantially pure barium hydride from impure barium metal contaminated with a metal impurity of lower boiling point, the improvement which comprises placing the impure barium metal in a retort, evacuating the retort to remove objectionable air, heating the barium-containing part of the 'retort above the melting point of said barium,

distilling the metal impurity but not the barium, selectively oxidizing the resulting metal impurity vapor by bringing it into reactive contact with a reducible metal oxide removed from the main body of `barium to be purified, collecting the oxidized metal impurity as a solid separate from the main body of barium to be purified, distilling and condensing the barium thus puried in a cooler part of the retort removed from the oxidized metal impurity, admitting hydrogen gas into the retort and continuing to supply hydrogen gas to the retort until the distilled and condensed barium is converted into the corresponding barium hydride.

24. In the method of producing substantially pure barium hydride from impure barium metal contaminated with a metal impurity of lower boiling point, the improvement which comprises placing the impure barium metal in a retort, evacuating the retort to remove objectionable air, heating the barium-containing part of the retort above the melting point of said barium, distilling the metal impurity but not the barium, selectively oxidizing the resulting metal impurity vapor by bringing it into reactive contact with a reducible metal oxide removed from the main body of barium to be puried, collecting the oxidized metal impurity as a solid separate from the main body of barium to be purified, distilling and condensing the barium thus puried in a cooler part of the retort removed from the oxidized metal impurity, admitting an inert gas and hydrogen gas into the retort, and continuing to supply hydrogen gas to the retort until the distilled and condensed barium is converted into the corresponding barium hydride.

25. In the method of producing substantially pure barium hydride from impure barium metal contaminated with a metal impurity of lower boiling point, the improvement which comprises placing the impure barium metal in a retort containing in its upper part a body of reducible metal oxide, evacuating the retort to remove objectionable air, heating the barium-containing part of the retort above the melting point of said barium, distilling the more volatile metal impurity but not the barium to be puriiied and absorbing the more volatile metal impurity by reaction with the metal oxide, distilling and condensing the less volatile barium thus purified in a cooler part of the retort removed from the oxidized metal impurity, admitting hydrogen gas into the retort and continuing to supply hydrogen gas to the retort until the distilled and condensed barium is converted into the corresponding barium hydrlde.

26. In themethod of producing substantially pure strontium hydride from impure strontium metal contaminated with a metal impurity o! lower boiling point, the improvement which comprises placing the impure strontium metal in a retort, evacuating the retort to remove objectionable air, heating the strontium-containing part of the retort above the melting point of said strontium, distilling the metal impurity but not the strontium, selectively oxidizing the resulting metal impurity vapor by bringing it into reactive contact with a reducible metal oxide removed from the main body of strontium to be purified, collecting the oxidized metal impurity as a solid separate from the main body of strontium to be purified, distilling and condensing the strontium thus puriiled in a cooler part of the retort removed from the oxidized metal impurity, admitting hydrogen gas into the retort and continuing to supply hydrogen gas to the retort until the distilled and condensed strontium is converted into the corresponding strontium hydride.

27. In the method of producing substantially pure strontium hydride from impure strontium metal contaminated with a metal impurity of lower boiling point, the improvement which comprises placing the impure strontium metal in a retort, evacuating the retort to remove objectionable air, heating the strontium-containing part of the retort above the melting point oi said strontium, distilling the metal impurity but not the strontium, selectively oxidizing the resulting metal impurity vapor by bringing it into reactive contact with a reducible metal oxide removed from the main body of strontium to be puriiled. collecting the oxidized metal impurity as a solid separate from the main body of strontium to be purified, distilling and condensing the strontium thus puriiied in a cooler part of the retort removed from the oxidized metal impurity, admitting an inert gas and hydrogen gas into the retort. and continuing to supply hydrogen gas to the retort until the distilled and condensed strontium is converted into the corresponding strontium hydride.

2s. In the method of producing substantially A pure strontium hydride from impure strontium metal contaminated with a metal impurity of lower boiling point, the improvement which comprises placing the impure strontium metal in a retort containing in its upper part a body of reducible metal oxide, evacuating the retort to remove objectionable air, heating the strontiumcontaining part of the retort above the melting point of said strontium, distilling the more volatile metal impurity but not the strontium to be puried and absorbing the more volatile metal impurity by reaction with the metal oxidel distilling and condensing the less volatile strontium thus puriiled in a cooler part of the retort removed from the oxidized metal impurity, admittins hydrogen gas into the retort and continuing to supply hydrogen gas to the retort until i0 the distilled and condensed strontium is converted into the corresponding strontium hydride.

PETER P. ALEXANDER. 

